This 21st round of the U.N. Conference of Parties (COP21) hopes for an agreement on reducing greenhouse gas emissions to hold the global temperature increase to 2 degrees Celsius above pre-industrial levels.

That’s an ambitious goal, mocked by some as idealistic, but there’s nothing wrong with ambition yoked to ideals. Still, goals also must be realistic, consistent with the laws of physics and chemistry, and honest about the possibilities within, and the impediments created by, the world’s economic and political systems.

Here’s one of the toughest parts of those realities we have to grapple with: Even if leaders produce a serious agreement with enforcement mechanisms, we will not be living in the same kind of world in which people created those social systems. The consequences of human recklessness define our future.

Even if pledges for emission reductions being discussed by world leaders were to be achieved, we are going to see potentially catastrophic global warming by the end of this century, and likely far earlier.

The scientific community’s consensus on climate change includes not only models about what likely will happen if we don’t curtail emissions, but the extent of the warming already locked in by past emissions and the intensifying effects of climate feedback loops.

Grieving is not surrender but an acceptance of what can’t be changed and a commitment to what can be accomplished, within limits the ecosphere sets.

And climate disruption is only one part of the story of ecological degradation. Predictions are a fool’s game, but look at any critical measure of the health of the ecosphere on which our lives depend—groundwater depletion, topsoil loss, chemical contamination, increased toxicity in our own bodies, the number and size of “dead zones” in the oceans, accelerating extinction of species and reduction of biodiversity—and ask a simple question: Are we heading in the right direction?

Whether or not we want to confront any of this politically, many people have at least a visceral sense of what is coming. If we want to begin shaping a livable future, we should start grieving, collectively, for what we have lost and likely will lose.

Grieving is not surrender but an acceptance of what can’t be changed and a commitment to what can be accomplished, within limits the ecosphere sets. We understand the importance of such grieving in personal contexts, when we lose loved ones, and now we need to apply it to the planet, together.

My friend Jim Koplin was the first person I knew who had faced these realities, decades ago, long before these crises were headline news. Jim was radicalized by the social movements of the 1960s and shaped by his rural roots in the dirt of the Depression-era farm on which he was born.

As he focused on social justice, critiquing the domination/subordination dynamic at the heart of exploitation within the human family, he was increasingly more alarmed about the effects of humans’ attempts to dominate the larger living world.

Because he refused to turn away from reality, later in his life Jim confided to his friends, “I wake up every morning in a state of profound grief.”

Jim wasn’t unhappy with his life or depressed. His grief, not only for people suffering but also for the destruction of the living systems of the world, didn’t lead him to retreat. Until he died at 79, Jim was actively engaged in political projects, public education efforts, and community organizing.

His capacity to face difficult truths was a source of strength, and so important to me that after his death I wrote a book about him, Plain Radical, offering his wisdom to those who never met him.

Jim helped me understand that there are no solutions to multiple, cascading ecological crises if we insist on maintaining the high-energy/high-technology existence lived in much of the industrialized world (and desired by many currently excluded from it).

Even many tough-minded activists willing to challenge unjust concentrations of wealth and power are reluctant to let go of a commitment to this so-called “lifestyle,” which has not produced a culture of life but a kind of death cult, a society that values cheap pleasures and cheap toys more than healthy people and a healthy planet.

When we refuse to grieve for what is passing away, we are more likely to cling irrationally to ways of living that cannot be sustained. When we cannot acknowledge the deep sorrow of what is lost, we scramble to hide from the reality of the loss and perpetuate the illusion that we can continue on this course.

That’s why a collective grieving process should be a priority for us all, helping us let go of the delusion that we can maintain unsustainable systems.

The technological fundamentalists—those who believe we can defy all limits and invent our way out of any crisis—will tell us we need to use our imaginations. I agree, but our task is not to imagine a narcissistic science-fiction future. A decent human future—perhaps the possibility of a human future at all—depends on our ability to imagine a new relationship to the larger living world.

• Robert Jensen is a professor in the School of Journalism at the University of Texas at Austin and board member of the Third Coast Activist Resource Center in Austin. He is the author of Plain Radical: Living, Loving, and Learning to Leave the Planet Gracefully (Counterpoint/Soft Skull, 2015).